


Tattered Control

by hyliank8



Series: Vampire Gaster AU Collection [1]
Category: Undertale (Video Game)
Genre: (essentially at least), Alternate Universe - Vampire, Angst, Betrayal of Trust, Blood Drinking, Established Sanster, Loss of Control, M/M, Magic Blood, Non-Consensual Blood Drinking, Sadism, Vampire W.D. Gaster (Undertale), W. D. Gaster is not related to Skelebros, sorta-Graphic Rape/Non-Con, unintentional tho
Language: English
Status: Completed
Published: 2020-05-23
Updated: 2020-05-23
Packaged: 2021-03-03 06:02:06
Rating: Mature
Warnings: Rape/Non-Con
Chapters: 1
Words: 2,962
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24329989
Author URL: https://archiveofourown.org/users/hyliank8/pseuds/hyliank8
Summary: Gaster's usually able to contain his thirst. Unfortunately, Sans gets in his way one time that he can't.(Vampire Gaster AU)
Relationships: Alphys & Sans (Undertale), W. D. Gaster/Sans
Series: Vampire Gaster AU Collection [1]
Series URL: https://archiveofourown.org/series/1922023
Comments: 18
Kudos: 87





	Tattered Control

**Author's Note:**

> this is inspired by a piece of art that one of my good friends made over on twitter! we’ve both been thinkin about vampire gaster a bit and then they drew somethin for it and their beautiful art immediately inspired me to write this ;-;
> 
> also heads up that this is one of those things that hurt my heart a lil to write, so pls mind the warnings. still a liiiiittle self-conscious abt posting noncon not gonna lie buT it's okAy it's finE
> 
> enjoy, hehe

“gaster,” Sans gasps. There’s barely room for him to move with the way Gaster has him suspended and trapped against the wall. He can’t stop his soul from fluttering with fear, can’t help the nervous sweat beading on his skull—he’s absolutely _terrified_. Gaster seemed fine all day, but when Sans visited his best friend in his office after normal work hours ended he noticed the ravenous gaze Gaster had fixed on him… and that was the only warning he had before Gaster seized him with effortless strength and sunk his sharp teeth into Sans’ collarbone. 

“s...stop,” Sans pleads, praying to the stars that some rational section of Gaster’s mind is still active. Sans has powerful magic—more powerful than most monsters his size surely, but if Gaster is insistent on draining him… “you’re losing control!”

Gaster releases his bite for a moment to run his tongue over the wound his teeth have left, using the pause in his feeding to reply. “Am I, Sans?” His voice is deep and dark, rumbling in his chest almost like a growl, predatory and unforgiving. It’s so unlike the voice Sans is used to Gaster addressing him with—hearing it sends helpless shivers down Sans’ spine. “I’m not sure I’m the one to blame when you’re the one who decided to be… particularly _enticing_ today.” 

Gaster trails his tongue up to Sans’ jaw, scraping his rough teeth against the bone. “I want you, Sans,” he hisses lowly, his breath scorching the side of Sans’ skull. The dark words send a blunt pulse of apprehension through Sans’ soul, and he cries out when Gaster sinks his teeth back into him. 

“gaster,” Sans tries again, his breath coming in quick, terrified pants despite his efforts to stave off his panic. “th-this isn’t you, c’mon, you gotta—you gotta let me go, i know you don’t really wanna hurt me—”

Gaster may as well have not heard him; he doesn’t respond, instead materializing a hand to pull at the waistband of Sans’ shorts. Cold dread sparks in Sans’ soul as Gaster shifts his delicate weight to allow the hand to pull the shorts off of him completely. The frigid air that immediately assaults his bare bones makes him shiver as he realizes what Gaster meant by _want_. Sans can do nothing to stop this, he has no leverage; Gaster’s holding him in the air, far away from anything he could use to ground himself or to push off of, and even if he did have something his strength would never be enough to overpower Gaster when he's driven by thirst. Not for the first time in his life, Sans curses his weakness and his small size.

Sans' soul stutters at the clink of a buckle as the magic hand moves down to undo Gaster’s belt.

“w-wait, d-don’t—!”

Gaster pushes inside of him, grunting around Sans’ clavicle at the same time that Sans whimpers.

“ _‘dings—!_ ” Oh god, maybe it doesn’t hurt as badly as it could but he feels so _full_ and his collarbone is _burning_ with pain and it’s all _too much—_

“Mmh, stars, so _tight_ ,” Gaster pants, his voice thick with lust as he releases Sans from his bite. “Such an extraordinary taste… and mine, you're _mine_ ,” Gaster punctuates his possessive growl with a thrust of his hips as he licks the magic blood oozing from his assistant’s wound, entirely ignoring Sans’ wince at his harsh treatment.

Gaster works up a rhythm grinding his hips against him as Sans whimpers at the heat that travels up his spine from the sensation. It hurts in a way he’s not used to; compared alongside the gentle intimacy he’s familiar with experiencing while joined with Gaster like this, it feels like this… can’t be real. And the pain is so _complicated_ because part of him wants it to feel good, wants what he normally has—Gaster caring about him, caring about making him feel good. The ache throbs not only in his pelvis but in his _soul_ , too. Is this, deep down at an instinctive level, all Gaster really wants him for? This wouldn’t have been the first time they’ve done this, but—Gaster always _asks_ , always does his best to make sure Sans is as comfortable as he can be. But now he’s just—just _taking_ what he wants without any concern for Sans being in pain, and that’s so unlike him in such a terrifying way. It's wrong, it's all _wrong_. How far gone must his rational thought be?

“a-ah!” Sans cries as Gaster eagerly latches onto the wound on his collarbone again. Gaster doesn’t sink his teeth in again, thank the stars, but the needy way he sucks his magic from the bite _hurts_. “gaster…!” 

The throb of his magic being taken from him is still sharp and intense, but Sans can’t help but notice it’s starting to numb around the edges; and while Gaster’s thrusts inside him are rough and needy, the heat from that sensation is dulling, too. He wants to be grateful for it, but he’s worried about what that could mean. His vision hazes, and he realizes with a sharp pulse of fear that he’s not sure how much magic he has left to support his eyesight. Without physical organs to provide function to his senses, he depends entirely on his magic to allow him to see—and to hear, to feel, to speak—and if he can’t stop his magic from draining, he realizes he’ll soon be entirely insensate, completely helpless to stop Gaster from taking his magic until he has nothing left to give.

Sans’ fingers twist into the fabric of the back of Gaster’s shirt with renewed desperation, pulling it as if that would be enough to force Gaster off of him. The attempt feels shaky, futile as it may have been regardless, and with a pit of terror in his soul Sans realizes how incredibly difficult it is to move his limbs voluntarily.

“hng, please—” Sans whimpers as Gaster continues licking and sucking at the gash, rocking into him at a harsh pace. He braces a hand against Gaster’s head and pushes desperately, anything to get him _off_ of him, but Gaster is locked onto him like a vice, mindlessly absorbed in the sea of his instincts. His strength seems hopeless to work against, and Sans’ hands shake as he frantically continues trying to pry Gaster off of him, desperation rising as his strength wanes. “y-you’re—you’re taking too much, i c-can’t— pl-please—”

Gaster groans as if in response to his helpless begging, giving a particularly rough thrust that drives Sans’ spine against the wall hard enough to knock him breathless for a moment.

Sans chokes back a dry sob at Gaster's cruel reaction. Is he… _enjoying_ feeling Sans struggle against him? The possibility is horrifying and throbs painfully in Sans' soul—the possibility that Gaster, his best friend, his lover, would _enjoy_ hurting him, enjoy his suffering, enjoy drinking his magic until he has nothing left for himself.

Sans’ vision clouds as his energy continues to diminish hopelessly. It takes too much strength to keep trying to push Gaster away, so Sans does what he does best—he gives up, letting his arms fall to his sides, resigning himself to letting Gaster use him until he’s satisfied.

Gaster moans into him at a pitch that Sans knows indicates that he’s close. _please let this end_ , Sans begs silently, _just come and be satisfied and stop drinking from me,_ _please_.

Gaster’s hips stutter to a halt as he comes, releasing Sans’ clavicle as he groans with the intensity of his orgasm. Magic blood drips steadily from Sans’ collarbone, staining his shirt and running down through his rib cage and onto the floor beneath him. 

“thank the stars,” Sans murmurs lethargically despite how gross he feels. He doesn’t care anymore, he can ignore the unpleasant way Gaster’s release sticks to his bones alongside his own blood as long as this dull pain from his feeding finally _stops_. “pl-please let me down now, gaster.”

Sans winces as Gaster pulls out of him and uses his magic hands to fix his own clothing. Sans is relieved at Gaster being done with him but still longs for Gaster to finally set him down; he’s so desperate to be on the ground and be in control of his own movement again that Gaster could drop him carelessly at this point, even throw him down and he’d still be grateful.

Sans feels Gaster shift his stance and turn around to walk with him, and Sans simply leans his weight against the larger monster, too drained of a fight to do much else. Relief floods through him when Gaster sets him on Gaster’s desk atop a layer of scattered papers.

That relief surges right back up into panic when Gaster interlocks their fingers, pushing his hands back and pinning them against the desk.

“wait, n-no—!” Gaster’s huge body cages him in as he leans down to Sans’ still-bleeding clavicle once again. Sans braces himself for the same pain as before, but he's caught off guard when Gaster’s sharpened teeth piece the bones of his neck instead.

Sans can’t help the weak, choked cry that is jarred from him as the pain flares anew, his spine arching off the desk. He gasps desperately, feebly trying to pull his arms free so he can push against Gaster’s chest, so he can get _away_ , but Gaster’s grip on his hands is iron. He knows he’s losing too much magic. His vision is fading again, becoming darker than before, and his body is starting to go numb. His collarbone still bleeds as Gaster drinks his magic in greedy gulps from the fresh wound on his neck.

“ ‘dings,” Sans gasps, his voice forming the name sluggishly. His soul flutters weakly as he makes another feeble, mindlessly desperate attempt at pulling his hands free. Gaster keeps him restrained effortlessly; he doesn’t seem to even notice Sans’ frail struggles. Sans isn’t sure how much more he can take. “it’s too m-much… you have to stop… pl...ease…”

Gaster doesn’t respond; Sans suspects he’s so immersed in his instincts by now that he’s not even heard him, his mind fixated solely on finishing his feeding. Sans squeezes Gaster’s hands hopelessly, desperate for him to break free from his mind and realize what he’s doing, _who_ he’s doing this to. He just wants him to _notice_ , feel his hands against his… the same hands he’s held so many times before, during experiment observations, after work, on the way to their bench in Waterfall.

“ga...ster,” Sans rasps weakly, his frail breath rattling delicately in his rib cage as he forces the words out. “pl...ease… it’s m...me… don’t… do thi...s…”

Sans is so out of it that he’s not sure when the tears started, but he’s aware of thick tracks of them rolling down the sides of his skull. Is this it? Is he going to be killed by his best friend, one of the people he thought he trusted most? His soul convulses painfully, too much of his magic drained for it to beat properly. 

Sans lets his hands fall slack, far too exhausted to continue clenching them around Gaster's. The painful shuddering of his fading soul is the last thing he feels before his vision is consumed by darkness.

—

Sans can’t feel anything.

It’s as though he’s drifting through space, no outside forces tampering with his senses. No physical feeling, no light, no up or down. Just the empty, endless void. ...Is he dead? Is this what being dead feels like? It’s interesting that Sans can’t bring himself to feel upset about it, can’t bring himself to feel any sort of emotion. He’s just… numb.

After what feels like an eternity floating in nothingness, a sound echoes into his awareness. A faint… beeping?

Dim, blurry light filters into his consciousness as the beeping becomes less distant. Gradually, his feeling returns. He’s comfortable, lying down on something soft, a pleasant warmth covering him. 

He cracks his eye sockets open and winces at the harsh, blurry light that assaults his vision.

“S-Sans?” Alphys’ voice is barely louder than the beeping. What’s she doing here? ...And where is _here,_ exactly?

As Sans opens his eyes the rest of the way, Alphys’ worried expression swims over him, coming into focus as the moments pass. He opens his mouth to try to respond, but the words get stuck in his throat. He blinks, focusing his sight, and glances around; vaguely, he recognizes his surroundings to be part of the lab’s recovery room. He’s never been the one in one of the cots before, and he reflects that it’s odd to see the room from this angle for the first time. He suspects the faint beeping is coming from a soul monitor.

He clears his throat to try to speak again. “heya, alph,” he manages. He shifts his weight, hoping to be able to sit up to see her better.

“W-wait, you should stay down,” Alphys quickly interjects. “You, uh… your s-soul’s still pretty unstable.”

“...unstable?” he echoes. Why is his soul unstable? Did something happen? Sans’ mind is a hazy mess of darkness, and searching his memories he finds his recent ones frustratingly just out of reach.

“U-uh, yeah, you know… when you lose a lot of magic your soul has a hard time f-functioning normally. You were, um, in a pretty r-rough state when Gaster brought you in.”

“gaster—?” Sans halts. 

Something about saying the name makes his soul twist.

_“gaster… s-stop—” Cold, hungry eyes, a strength he can’t fight against, an attacker who won’t listen no matter how much he begs it’s hopeless gaster please stop it hurts don’t do this—_

“oh, god.” Now that he remembers, he wishes he couldn’t. His soul constricts, the faint beeping in the room speeding up for a moment in response. “he lost control.”

Alphys nods, a troubled look on her face.

“He was pretty, um, d-distraught bringing you in here. He kinda just kept s-saying ‘sorry’ over and over again, I couldn’t really m-make out much of anything else he was trying to say. I’ve n-never seen him, um, apologize, or cry before, at least n-not like… that.”

“he was crying?” Despite himself, Sans’ soul clenches at the thought. “where is he now?”

“He’s taking a w-walk, I think.”

“on his own?” Sans can’t keep the worry out of his voice. He knows Gaster’s penchant to deal with his guilt in self-destructive ways, and if he’d really been that distressed— 

“N-no, no,” Alphys quickly reassures him. “Doctor Anthony is looking out for him to make sure he won’t do anything reckless.”

Sans sighs lightly with relief. “that’s good.” Sans will have to thank the tall cat monster later. They’re close to Gaster for sure, but keeping Gaster from tearing himself to pieces over his guilt is no easy task for a colleague.

“But, u-um, I should tell you that I attached an IV to your soul to replenish its magic supply directly. I, um, would have tried something else first but y-you had some really, r-really low magic levels… you might have to stay in here for another day to m-make sure it replenishes completely, or it could become unstable again.”

He nods in acknowledgment. He thought he felt something odd about his soul, now that he thinks about it, but he supposes he just assumed it was because of his lack of magic. “thanks, alph. ‘preciate it.”

“N-no problem. I also put some healing salve on th-the, um, bites. They were kinda… messy, and… deeper than I would have expected, so that could have caused your m-magic to drain faster. There was a l-lot of blood...” Alphys trails off into silence for a moment, a contemplative expression on her face before she continues. “...D-do you know what made him lose control like that?” 

Sans’ teeth clench, and he averts his gaze, opting to stare back up at the ceiling instead.

“i’m... not sure, honestly,” he says, a tightness wedging its way into his voice despite his best efforts. “he seemed fine all day, i dunno, but then i went into his office to talk to him after work and... a-and—” _and he pinned me against a wall and drank from me and_ _used_ _me and wouldn’t stop no matter how much i pleaded, no matter how much i begged him to let me go._

Sans squeezes his eyes shut to dispel the hot tears he feels pricking at the corners of his eye sockets.

“S-sorry, sorry,” Alphys says quickly. “We don’t have to talk about it now. I’m sure you’re e-exhausted. Um... w-would you like me to stay with you until you fall asleep?”  
  
Sans nods, opening his eyes but still carefully watching the ceiling. “please.” He really doesn’t want to be alone with his thoughts right now.

“Alright, I’m just gonna, um, fill out some reports," Sans hears the rustle of her lab coat and assumes she's made a gesture to the desk on the other side of the room. "So j-just let me know if you need something, okay?”

“...thanks, alph. i really appreciate you bein’ here.”

“O-of course.” There's a little optimistic note to her voice—no doubt she's simply happy to be helpful. Sans smiles lightly; Alphys is a good friend.

Sans closes his eyes and shifts to make himself more comfortable as Alphys retreats to the desk to work. He prays that he’ll be able to fall into another dreamless sleep. 

And when sleep eludes him, he finds his soul tensing as he makes a tremendous effort to think about anything but the cold, piercing gaze of his best friend.

**Author's Note:**

> >:]
> 
> i have another fic in the works rn with a more Intentionally Evil version of vampire gaster hehe ,, so hopefully that'll b up at some point within the next few weeks :eyes emoji: (and, i did post a smol pic preview of it on Twitter if ur curious)
> 
> as always u can find me on [tumblr](https://hyliantimelordin221b.tumblr.com) (mostly sfw, though tbh my self-control is slowly waning w/ that) and [twitter (nsfw)](https://twitter.com/K8Maybe)!
> 
> feel free to lemme know what you thought ^^


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